Abstract
In this work, we report on self-limiting growth of InN thin films at substrate temperatures as low as 200 °C by hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD). The precursors used in growth experiments were trimethylindium (TMI) and N2 plasma. Process parameters including TMI pulse time, N2 plasma exposure time, purge time, and deposition temperature have been optimized for self-limiting growth of InN with in ALD window. With the increase in exposure time of N2 plasma from 40 s to 100 s at 200 °C, growth rate showed a significant decrease from 1.60 to 0.64 Å/cycle. At 200 °C, growth rate saturated as 0.64 Å/cycle for TMI dose starting from 0.07 s. Structural, optical, and morphological characterization of InN were carried out in detail. X-ray diffraction measurements revealed the hexagonal wurtzite crystalline structure of the grown InN films. Refractive index of the InN film deposited at 200 °C was found to be 2.66 at 650 nm. 48 nm-thick InN films exhibited relatively smooth surfaces with Rms surface roughness values of 0.98 nm, while the film density was extracted as 6.30 g/cm3. X-ray photoelectron spectroscopy (XPS) measurements depicted the peaks of indium, nitrogen, carbon, and oxygen on the film surface and quantitative information revealed that films are nearly stoichiometric with rather low impurity content. In3d and N1s high-resolution scans confirmed the presence of InN with peaks located at 443.5 and 396.8 eV, respectively. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) further confirmed the polycrystalline structure of InN thin films and elemental mapping revealed uniform distribution of indium and nitrogen along the scanned area of the InN film. Spectral absorption measurements exhibited an optical band edge around 1.9 eV. Our findings demonstrate that HCPA-ALD might be a promising technique to grow crystalline wurtzite InN thin films at low substrate temperatures.
Highlights
Among the III-nitride compound semiconductor materials family, indium nitride (InN) has attracted much attention due to its largest electron saturation velocity, highest mobility, smallest direct band gap, and smallest electron effective mass
We report on self-limiting growth of InN thin films at substrate temperatures as low as 200 ◦C by hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD)
Growth rate remained constant as 0.64 Å/cycle with 120 s of N2 plasma exposure time, which shows that 100 s of N2 plasma exposure time is enough to saturate InN growth rate
Summary
Taking cost and CMOScompatibility advantages into consideration, InN has been grown on Si(100) using MBE,[26] femto second pulsed laser depositon,[22] and laser assisted CVD.[27] As high-temperature growth methods further pose conflicts with existing CMOS technology, atomic layer deposition presents an alternative strategy to grow III-nitride films on Si substrates at low temperatures. Process parameters including TMI pulse time, N2 plasma exposure time, purge time, and deposition temperature have been optimized for self-limiting growth of InN. Impact of these process parameters on film quality has been investigated and described in detail. Structural, optical, and morphological characterization of the grown InN thin films were performed and presented
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